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From Jimmy Mårdell (JIRA) <>
Subject [jira] [Commented] (CASSANDRA-8193) Multi-DC parallel snapshot repair
Date Fri, 14 Nov 2014 17:51:34 GMT


Jimmy Mårdell commented on CASSANDRA-8193:

New patched added. I've added an enum for specifying the degree of parallelism. This cascaded
up in the code path a bit. Backward compatibility should be maintained, at the expense of
adding a few more forceRepair methods in StorageService.

As a side note, can't we remove many of forceRepair methods in StorageServiceMBean in 2.1?
It's getting quite ugly. nodetool only uses two of them (one with range and one without range).

> Multi-DC parallel snapshot repair
> ---------------------------------
>                 Key: CASSANDRA-8193
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jimmy Mårdell
>            Assignee: Jimmy Mårdell
>            Priority: Minor
>             Fix For: 2.0.12
>         Attachments: cassandra-2.0-8193-1.txt, cassandra-2.0-8193-2.txt
> The current behaviour of snapshot repair is to let one node at a time calculate a merkle
tree. This is to ensure only one node at a time is doing the expensive calculation. The drawback
is that it takes even longer time to do the merkle tree calculation.
> In a multi-DC setup, I think it would make more sense to have one node in each DC calculate
the merkle tree at the same time. This would yield a significant improvement when you have
many data centers.
> I'm not sure how relevant this is in 2.1, but I don't see us upgrading to 2.1 any time
soon. Unless there is an obvious drawback that I'm missing, I'd like to implement this in
the 2.0 branch.

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